While dynamic seal design has been given much attention, the simpler matter of designing a good static seal is still not finalized. Static seals, as opposed to dynamic seals, can be pressed hard against the surface to be sealed. Such pressure is often used to retain two pipe ends in a pipe coupling and thus to provide a mechanical leak-proof joint. The coupling, and the flexible seal element used therein, and the sheet-metal housing containing the seal and applying pressure thereto, was disclosed in my previous U.S. Pat. No. 6,293,556, which is hereby incorporated in the present specification.
The seal element described in my previous patent is a ring having a cross-section which in approximate or simplified terms can be represented by a square. As is known, shape distortion occurs when a flexible element is compressed between a pair of rigid parallel surfaces. On compression such seal element will take the form of a squat barrel having a flat upper and lower faces and an outwardly curved sidewall, as will be seen in FIG. 1. The curved sidewall however does not seal well against a flat flange, allowing some leakage of high pressure fluids of low-viscosity. The resulting leakage path leads from the flange of the coupling, around the edge of the U-channel and onto the outer face of the U channel itself.
In U.S. Pat. No. 4,909,519 Anderson discloses a pressure-resistant system for joining concrete pipes end to end. The seal is retained by internal ribs extending into the cement.
Brancher, in U.S. Pat. No. 5,501,472 discloses a compression seal for conduits passing through watertight barriers, such as containment sumps for underground gasoline storage. The seal is much exposed to the stored liquid and is likely to fail under pressure.
The gland seal assembly disclosed by Burgess in U.S. Pat. No. 5,772,218 features axial compression means to achieve radial compression of the packing rings. The rings are square sectioned. As this is a dynamic seal, little pressure is applied to the revolvable shaft and the minor seal geometry distortion which results is used for shaft sealing.
In U.S. Pat. No. 6,152,494 Corbett Sr., et al. describe and claim a pipe gasket with combined lip and compression seal geometry. The seal is not subjected to high pressure, as it is inserted into a groove within a socket end of a thermoplastic pipe and the projections provided are intended for sealing against the outer diameter of the pipe.